Acoustic Localization Systems Research Articles

Design of a complete simulator for underwater acoustic localization systems based on spread-spectrum signals

Deploying prototype positioning systems in underwater environments is expensive and an especially challenging task, so a first common approach is to carry out simulated studies to evaluate the requirements and restrictions imposed by the environment. In this regard, it is helpful to have simulation models that allow the generation of a wide range of tests as a previous step to any experimental prototype implementation. For that purpose, this work focuses on the design of a simulation tool that facilitates research on underwater positioning systems by considering several parameters and features, such as the design of the signals emitted by the acoustic transducers (encoding techniques, modulation schemes, etc.), the frequency response and location of emitters and hydrophones, the bathymetry of the seabed, and the channel effects on the ultrasonic signal propagation, implemented in a model based on ray tracing for the propagation of acoustic signals. The simulation tool has been validated through a complete set of tests for different configurations and situations, analyzing the signals involved at different processing stages: baseband, modulated signals, received signals, and final estimated positions. This simulation tool is a valuable asset to research different positioning system configurations or to illustrate several concepts in a pedagogical context.

Localizing wild chimpanzees with passive acoustics

Localizing wildlife contributes in multiple ways to species conservation. Data on animal locations can reveal elements of social behavior, habitat use, population dynamics, and be useful in calculating population density. Acoustic localization systems (ALS) are a non‐invasive method widely used in the marine sciences but not well established and rarely employed for terrestrial species.We deployed an acoustic array in a mountainous environment with heterogeneous vegetation, comprised of four custom‐built GPS synchronized acoustic sensors at about 500 m intervals in Issa Valley, western Tanzania, covering an area of nearly 2 km2. Our goal was to assess the precision and error of the estimated locations by conducting playback tests, but also by comparing the estimated locations of wild chimpanzee calls with their true locations obtained in parallel during follows of individual chimpanzees. We assessed the factors influencing localization error, such as wind speed and temperature, which fluctuate during the day and are known to affect sound transmission.We localized 282 playback sounds and found that the mean localization error was 27 ± 21.8 m. Localization was less prone to error and more precise during early mornings (6:30 h) compared to other periods. We further localized 22 wild chimpanzee loud calls within 52 m of the location of a researcher closely following the calling individuals.We demonstrate that acoustic localization is a powerful tool for chimpanzee monitoring, with multiple behavioral and conservation applications. Its applicability in studying social dynamics and revealing density estimation among many others, especially but not exclusively for loud calling species, provides an efficient way of monitoring populations and informing conservation plans to mediate species loss.

Broadband Acoustic Communication Aided Underwater Inertial Navigation System

We present an underwater localization system for medium-sized Autonomous Underwater Vehicles (AUVs) that leverages a broadband wireless acoustic communication system for GPS-denied underwater localization. Many current acoustic localization systems assume a single line-of-sight path and use either narrow-band signals or short-duration pings for the convenience of mitigating motion-induced Doppler at the expense of the time-of-arrival (TOA) accuracy and operational flexibility. We propose a novel acoustic localization system that utilizes the aggressive signal processing embedded in underwater acoustic communication systems to resolve multi-path and Doppler distortion and finely estimate timing information using broadband communication signals. Timing and Doppler information extracted from this process is then used to estimate biases and drift from an inertial navigation system (INS) using a Bayesian framework. To demonstrate the feasibility of the system model, co-simulations are created from the MACE10 experimental data. Our results show dramatic improvement in localization accuracy, with an error of less than 120 m achieved over the 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 7 km distance range from the MACE 10 experiment between an AUV and a remote beacon with an acoustic communication transmission interval of 30 seconds.

Information Communication Technology (ICT) Tools for Preservation of Underwater Environment: A Vision-Based Posidonia Oceanica Monitoring

Abstract Underwater monitoring activities are crucial for the preservation of marine ecosystems. Currently, scuba divers are involved in data collection campaigns that are repetitive, dangerous, and expensive. This article describes the application of Information Communication Technology (ICT) tools to underwater visual data for monitoring purposes. The data refer to a Posidonia Oceanica survey mission carried out by a scuba diver using a Smart Dive Scooter equipped with visual acquisition and acoustic localization systems. An acoustic-based strategy for geo-referencing of the optical dataset is reported. It exploits the synchronization between the audio track extracted from a camera and the transponder pings adopted for the acoustic positioning. The positioning measurements are employed within an extended Kalman filter to estimate the diver's path during the mission. A visual odometry algorithm is implemented within the filter to refine the navigation state estimation of the diver with respect to the acoustic positioning only. Moreover, a smoothing step based on the Rauch-Tung-Striebel smoother is applied to further improve the estimated diver's positions. Finally, the article reports the results of two different data processing for monitoring applications. The first one is an image mosaicking obtained by concatenating subsequent frames, whereas the second one refers to a qualitative distribution of the Posidonia Oceanica over the mission area accomplished through an image segmentation process. The two outcomes are plotted over a satellite image of the surveyed area, showing that the proposed process is an effective tool capable of facilitating divers in their monitoring and inspection activities.

Accurate Localization in Acoustic Underwater Localization Systems.

In underwater localization systems several sources of error may impact in different ways the accuracy of the final position estimates. Through simulations and statistical analysis it is possible to identify and characterize such sources of error and their relative importance. This is especially of use when an accurate localization system has to be designed within required accuracy prescriptions. This approach allows one to also investigate how much these sources of error influence the final position estimates achieved by an Extended Kalman Filter (EKF). This paper presents the results of experiments designed in a virtual environment used to simulate real acoustic underwater localization systems. The paper intends to analyze the main parameters that significantly influence the position estimates achieved by a Short Baseline (SBL) system. Specifically, the results of this analysis are presented for a proprietary localization system constituted by a surface platform equipped with four acoustic transducers used for the localization of an underwater target. The simulator here presented has the purpose of simulating the hardware system and modifying some of its design parameters, such as the base-line length and the errors on the GPS and Inertial Measurement Unit (IMU) units, in order to understand which parameters have to modify for improving the accuracy of the entire positioning system. It is shown that statistical analysis techniques can be of help in determining the best values of these parameters that permit to improve the performance of a real hardware system.

Određivanje pozicije akustičkih izvora korišćenjem spektralne analize višeg reda za određivanje vremena nailaska signala

The localization of various acoustic sources in a battlefield (such as weapon rounds, mortars, rockets, mines, improvised explosive devices, vehicle-borne improvised explosive devices and airborne vehicles) nowadays has a significant history. In acoustic source localization systems of multiple sensors, networked and placed at known positions are used to detect signals emitted from the source and perform localization of the source. Time of arrival estimation of the gun fire shock waves at large distances is significant when the purpose is the gun localization. At large distances shock wave signal is significantly deformed and therefore it is relatively difficult to accurately estimate the time of arrival. In this paper methods for TOA estimation are proposed, which are based on cumulants of the acoustic signal which originate from distant gunfire events. Localization of acoustic sources is performed in two steps by time difference estimation of acoustic signal arrival and using Discrete Probability Density method for positioning. Numerous field experiments have been conducted in order to verify performance of the proposed approach.

Određivanje pozicije akustičnih izvora korišćenjem metode diskretne raspodele verovatnoća podržane združenom detekcijom i procenom vremena nailaska signala

The localization of various acoustic sources in a battlefield (such as weapon rounds, mortars, rockets, mines, improvised explosive devices, vehicle-borne improvised explosive devices and airborne vehicles) nowadays has significant history. In acoustic source localization systems multiple sensors (such as microphones or microphone arrays), placed at known positions and networked, are used to detect signals emitted from the source and perform localization of the source. In this paper, Discrete Probability Density (DPD) method, as a method for position determination, has been used to estimate location of acoustic sources such as artillery weapons. Wavelet decomposition of the acoustic signal enables to emphasize N-wave in the time domain. Time of Arrival (TOA) estimation is realized by a statistical analysis of narrow time segment which hold N-wave. Based on the estimated TOA Time Difference of Arrival (TDOA) is calculated. TDOA presents relative time difference of arrival of the sound signal between pairs of sensors. Localization of the acoustic sources is performed by time difference estimation of acoustic signal arrivals using Discrete Probability Density method. A number of experiments with fire off mortar projectiles have been conducted in order to verify the performance of the proposed approach.

A real-time array calibration method for underwater acoustic flexible sensor array

To solve the precise passive ranging problem of underwater acoustic localization systems, we design a large aperture flexible sensor array whose sensors are deployed without rigid connections. We propose a novel real-time array calibration method to estimate the 3-D coordinates of the sensors. Spherical interpolation estimator is used to estimate the range of the acoustic source. The impact of the estimation errors in time-delay and sensor coordinates on the spherical interpolation range estimator is analyzed via computer simulations. By comparing the passive acoustic ranging results from sea trials with the GPS measurement data, we show that the proposed method can calibrate the flexible array in real time more accurately and estimate the underwater acoustic source range precisely.

Visualization of multiple array acoustic source localization

Transient acoustic events such as gunfire, rocket launches, and explosions can be located using triangulation with multiple lines-of-bearing (LOBs) generated by distributed acoustic microphone arrays. The Army has fielded diverse sound localization and ranging systems that work well in open field environments, but suffer reduced performance in urban environments where echoes, multipath, diffraction, and blockages modify both the signatures and the propagation path. This demonstration will use light projected through a water basin to a screen to show traveling waves (ripple diffraction patterns) from transient events and how those wavefronts pass differently across the distributed array locations. The observers will gain an understanding of how multiple microphone elements in a small cluster of microphones (an array) can derive time-difference-of-arrival (TDOA) estimates to create array LOBs, as well as an introduction to triangulation through multiple distributed array LOBs. Objects simulating walls and buildings will be placed in the basin to demonstrate how complex waveforms and propagation paths can decrease the accuracy of acoustic localization systems.

On the performance of multi-GPU-based expert systems for acoustic localization involving massive microphone arrays

Sound source localization is an important topic in expert systems involving microphone arrays, such as automatic camera steering systems, human–machine interaction, video gaming or audio surveillance. The Steered Response Power with Phase Transform (SRP-PHAT) algorithm is a well-known approach for sound source localization due to its robust performance in noisy and reverberant environments. This algorithm analyzes the sound power captured by an acoustic beamformer on a defined spatial grid, estimating the source location as the point that maximizes the output power. Since localization accuracy can be improved by using high-resolution spatial grids and a high number of microphones, accurate acoustic localization systems require high computational power. Graphics Processing Units (GPUs) are highly parallel programmable co-processors that provide massive computation when the needed operations are properly parallelized. Emerging GPUs offer multiple parallelism levels; however, properly managing their computational resources becomes a very challenging task. In fact, management issues become even more difficult when multiple GPUs are involved, adding one more level of parallelism. In this paper, the performance of an acoustic source localization system using distributed microphones is analyzed over a massive multichannel processing framework in a multi-GPU system. The paper evaluates and points out the influence that the number of microphones and the available computational resources have in the overall system performance. Several acoustic environments are considered to show the impact that noise and reverberation have in the localization accuracy and how the use of massive microphone systems combined with parallelized GPU algorithms can help to mitigate substantially adverse acoustic effects. In this context, the proposed implementation is able to work in real time with high-resolution spatial grids and using up to 48 microphones. These results confirm the advantages of suitable GPU architectures in the development of real-time massive acoustic signal processing systems.

A Lightweight Collaborative Fault Tolerant Target Localization System for Wireless Sensor Networks

Efficient target localization in wireless sensor networks is a complex and challenging task. Many past assumptions for target localization are not valid for wireless sensor networks. Limited hardware resources, energy conservation, and noise disruption due to wireless channel contention and instrumentation noise pose new constraints on designers nowadays. In this work, a lightweight acoustic target localization system for wireless sensor networks based on time difference of arrival (TDOA) is presented. When an event is detected, each sensor belonging to a group calculates an estimate of the target's location. A fuzzyART data fusion center detects errors and fuses estimates according to a decision tree based on spatial correlation and consensus vote. Moreover, a MAC protocol for wireless sensor networks (EB-MAC) is developed which is tailored for event-based systems that characterizes acoustic target localization systems. The system was implemented on MicaZ motes with TinyOS and a PIC 18F8720 microcontroller board as a coprocessor. Errors were detected and eliminated hence acquiring a fault tolerant operation. Furthermore, EB-MAC provided a reliable communication platform where high channel contention was lowered while maintaining high throughput.

Food-related bray calls in wild bottlenose dolphins (Tursiops truncatus).

Because cetaceans are difficult to study in the wild, little is known about how they use their sounds in their natural environment. Only the recent development of passive acoustic localization systems has enabled observations of the communication behaviour of individuals for correlation with their surface behaviour. Using such a system, I show that bottlenose dolphins in the Moray Firth, Scotland, produce low-frequency bray calls which are clearly correlated with feeding on salmonids. The production of these calls is followed by fast approaches by conspecifics in the area. In animals which use sound as a foraging tool, it is difficult to distinguish between food calls which have evolved because of their role in attracting conspecifics, and food manipulation or searching calls which may attract conspecifics as a by-product. However, the low-frequency structure of the bottlenose dolphin bray suggests that it evolved because of a role in manipulating prey rather than in attracting conspecifics. This conclusion suggests that dolphins exploit the perceptual systems of their prey to facilitate capture.